Calkins has recently found that the vitality within a cycle is rhythmical, with alternations of more and of less frequent fissions, under the same set of conditions; and that minute doses of beef-tea or various mineral salts will not only keep up the higher rate, but even stave off senescence. Minute doses of alcohol will keep up the higher rate, but not avert senescence. He considers that Maupas' generalisations are in most respects too sweeping (Arch. Entw. xv. 1902, p. 139). But Dr. James Y. Simpson informs me that the possibility of stimulative regeneration has been found to be limited. See also Calkins and Lieb, Arch. Prot. i. 1902, p. 355.
As inferred by Hickson from the prolongation of the union.
When there are at the outset two or more micronuclei all undergo the first two fissions, but only one undergoes the third.
Zeitschr. wiss. Zool. xxxiii. 1880, p. 439.
Bezzenberger has given a key to the species of these two genera in Arch. Prot. iii. 1903, pp. 149, 157.